To determine whether tenidap, when compared to conventional non- steroidal anti-inflammatory drug (piroxicam), relieves symptoms of knee osteoarthritis (OA) and also regards the cartilage degeneration of OA, qualifying patients with knee OA will be randomized to receive piroxicam or one of two tenidap dosages over one year. Each patient will undergo needle arthroscopy to assess cartilage at entry and at completion.